Outdoor Wood Furnace Info
All-Purpose OWF Discussions => Plumbing => Topic started by: woodman on February 02, 2013, 08:14:53 PM
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Ok plumming experts, here is my question. I have 3 hx's in a series. The first pulls 10 degrees, the second pulls 20 and the third pulls another 10. Not often do all 3 call for heat at the same time, but when they do how am I suppose to keep return temps up. If it was set up off a manifold it would be no different unless it would only allow 1 zone to circulate at a time, right?
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Is the water heater also in the same series??
Is one of them rarely used?
I get nervous when I see folks do 2 and a plate, only thing that makes it ok sometimes is the up stairs one rarely kicks on
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The first is dhw, then the main furnace, and finally the garage. Mornings are probably peak demand with showers, the house coming up to temp, and the garage opening a couple of times.
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What size pump are you running?
Have you ever checked return temps when all 3 were running?
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Its a Bell and Gosset 36. No I havent checked when all 3 are calling for heat.
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That would be interesting to see that,
May be a good test
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Assuming it is 40ish what would be the fix?
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More flow would be the simplest
Bigger pump, or another in series
If your over 140 your fine, plus it would be a rare occassion
I just think it's gonna be under 140 with all 3 cranking
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I am pretty sure it will be under 140 at some point of the cycle, but like you said, it is rare for it to happen and I really don't like the idea of a bigger/extra pump. Since it is probably happening when the wood is mostly gone, or has at least went threw multiple burn cycles, would that cut down on the moisture available in the firebox?
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Yea it would def help that situation
Check it at different times so you'll know tho
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OK I will check temps tomorrow.
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With all 3 running I am pulling a delta t of 43*. I went out and looked inside of boiler, I couldn't see any signs condensation. Is it obvious to see, or does it form behind the creosolt?
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It's not always obvious to see, but you are probably ok,
I think the pl36 is helping you out and keeping you out of danger for the most part
As long as it is a rare occurrence
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Maybe I am off on this but if all 3 HX's are in series wouldn't it be better to have a loop with closely spaced tees tying them all together?
I don't know for sure, but it seems like that would make the water slow down even more, and the water would be even colder after it went through the hx's on its way back to the boiler. The only way I see around this is to put a buffer tank in the basement with multiple ports. Then plumb each hx on its own zone with its own circulator and zone valve. I don't like the cost and complexity of that thought though. In all honesty I was never worried about any of this until all the threads about boiler failure and low return temps.
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Close space tees would keep flow up, but were talking more pumps and all that, nahh
You could however use an aquastat on the last heat exchanger in the garage that would only allow your garage to be heated when the water temp was let's say 155 or higher, for example if the strap on had 140 degree water already coming to it, it wouldn't allow the garage to call for heat until it was a safe number
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WOuld one of those return line mixing valves back at the Boiler work for this off of the supply ? Ive been thinking about doing installing something like that this summer as im sure Ive got the same issue from time to time.
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Why not just put a relay on the house blower that disables the garage? Would that cause any other problems?
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why not put a bypass on the domestic tank and send more hot water back to the OWB..you could throttle back teh flow to the domestic water untill you were hardly adding any cold at the shower
perhaps the way it is now you are heating yoru hot water to say 140 or 150 and adding a bunch of cold at the shower..if you were to send less water through the plate exhanger and only heeated yoru domestic water to say 130 that would dtill be pleany of heat for the domestic use and you would be sending mcuh hotter water through the system?
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Maybe I am off on this but if all 3 HX's are in series wouldn't it be better to have a loop with closely spaced tees tying them all together?
this is a good idea and i don't knwo if you need more pumps? i run furnace plenum(8 or 10 feet of 3/4 copper)...domestic water(25 feet of 3/4 copper) ...exchanger in my fire place (50 feet of 1/2 pex) and 8 feet (1/2 pex) to floor heat (there is a pump to circulate teh floor heat) these footages are all one way so you have to double it to get back to the return header. I have 250 feet one way of 1 inch pexal pex to the boiler running a taco 11 pump and i have never run out of heat and never went below 150 return. i have a sepert line from the header to each appliance.
i know that the velociity (gpm) is slowed to each appliance, but they are all getting the same temp of water so i think that helps keep the return water hotter.
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Close t's would require a pump in the supply of thst appliance
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How much pipe was added to the main loop for the garage? If it is very much, putting that on a secondary loop with a small pump would cut the head pressure down and get better flow.
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The idea of a manifold and multiple pumps has been brought up a few times. I currently have everything set up in a series with 1" line, with a single pump at the boiler.
If I set it up with a manifold as 3 seperate zones, each with its own zone valve and pump, if all 3 were calling for heat can the 1" logstor supply enough water to each pump?
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It would probably work fine but I don't recommend putting the plate on a manifold. Everything should run through it first then split if you want to.
If you didn't have to add much pipe for the 3rd heat exchanger then the only thing putting them in parallel will really do is allow you to send more heat to one than the other.
If everything is working good and all you want to do is keep the temperature from dropping so much when all 3 are running at the same time, just either put an aquastat on the pipe that shuts off the garage blower if the temp goes under 150 or put a relay on it to keep it from running when the other blower is running.
Both very simple and doesn't require any plumbing changes.
If you do have a lot of pipe going to the 3rd heat exchanger then I would consider putting it on a secondary loop. (not manifold setup) For a secondary loop you put two closely spaced tees in the same pipe and add a pump that runs when the blower does. The water will completely bypass this loop when not calling for heat.